Detection of millimetric deformation using a terrestrial laser scanner: experiment and application to a rockfall event

Journal

Natural Hazards and Earth System Science

Author(s)

AbellánA., JaboyedoffM., OppikoferT., VilaplanaJ. M.

ISSN

1561-8633

Publication state

Published

Issued date

2009

Peer-reviewed

Oui

Volume

9

Number

2

Pages

365-372

Language

english

Abstract

Abstract. Terrestrial laser scanning (TLS) is one of the mostpromising surveying techniques for rockslope characteriza-tion and monitoring. Landslide and rockfall movements canbe detected by means of comparison of sequential scans. Oneof the most pressing challenges of natural hazards is com-bined temporal and spatial prediction of rockfall. An outdoorexperiment was performed to ascertain whether the TLS in-strumental error is small enough to enable detection of pre-cursory displacements of millimetric magnitude. This con-sists of a known displacement of three objects relative to astable surface. Results show that millimetric changes cannotbe detected by the analysis of the unprocessed datasets. Dis-placement measurement are improved considerably by ap-plying Nearest Neighbour (NN) averaging, which reducesthe error (1σ ) up to a factor of 6. This technique was ap-plied to displacements prior to the April 2007 rockfall eventat Castellfollit de la Roca, Spain. The maximum precursorydisplacement measured was 45 mm, approximately 2.5 timesthe standard deviation of the model comparison, hamperingthe distinction between actual displacement and instrumen-tal error using conventional methodologies. Encouragingly,the precursory displacement was clearly detected by apply-ing the NN averaging method. These results show that mil-limetric displacements prior to failure can be detected usingTLS.